How many hens do I need to keep 3 roosters happy???

Hello, all you fellow chicken friends!
Okay, here's my problem:
We inherited 4 chicks from our son's Kindergarden class back in May, and now it turns out that 3 of them are roosters (barred rocks). We've been trying to find good homes for 2 of them (Chuck and Luck), but to no avail. Our 6 year old insists that they not be cooked (we don't really want to, either...), and so now we're actually considering purchasing some hens for them, so that we can keep them all. My question is, what's the minimum amount of hens I can get away with? They're free range in our front yard, have plenty of space to spread out and get away from each other, and I'm having a larger house built for them this week, which will accomodate about 12 or so inhabitants at night.
Please give me some advice, this is our first time having chickens, and we are really in a jam right now, because the boys are 4 1/2 months old now, just started crowing, and are starting to look funny at Frieda, our only hen........

 

Oh my god, we are in soooooooooo much trouble...!

 

Okay, got another qustion: how about all these people who just have 1 rooster with 1 or two hens, and they seem to be doing just fine? There's a guy at a local feed store who has a roo and his girl living right there in the store, and she does not have a bare back... . Any thoughts...? I know I'm reachin', but maybe there's a way...?